Conventional techniques have been used for preparing articles featuring images which are revealed or formed by heat or light energy after manufacture. U.S. Pat. No. 736,035 to Stevenson, for instance, discloses an article featuring an image with a cover print layer, which print layer becomes transparent after exposure to light to reveal the image. U.S. Pat. No. 1,167,566 to Jenkins discloses similar techniques for railway transfer tickets.
Other techniques involve thermosensitive layers formed of leuco dyes, acids and/or other materials, which change color when exposed to heat or steam in order to betray tampering with or "candling" lottery tickets and other particles. U.S. Pat. No. 4,738,472 to Shibata discloses a label with such a layer that discolors upon attempts to remove the label using heat or steam. Similarly, U.S Pat. Nos. 4,407,443 and 4,488,646 to McCorkle disclose blush coatings for lottery tickets which betray exposure to solvents or heat. Polymeric molecules in those coatings coalesce and become more compact and thus more translucent to reveal such abuse.
In a similar vein, game pieces, lottery tickets and similar materials have been marketed with thermosetting layers covered by, among other layers, scratch off layers. According to U.S. Pat. No. 4,677,553 to Roberts, et al., for instance, a thermal printer at point of sale fixes information in such a thermosetting varnish coat, which may be subsequently exposed by removing the scratch off layer with a coin or a fingernail. U.S. Pat. No. 4,850,618 to Halliday similarly discloses lottery tickets which include thermally sensitive materials covered by one or more ruboff layers, which, as in the Roberts patent, may be printed at point of sale using a thermal printer and then revealed to the customer upon removal of the ruboff layer.
In addition, many techniques and processes exist for the preparation of thermally sensitive paper sometimes used in thermal printers for personal computers, copier machines and telecopy machines and similar devices. Such thermal papers may employ leuco, diazo, or metallic dyes or coatings. One typical system employs a leuco dye evenly dispersed in a binder with a developer material. The leuco dye and developer fuse or react to generate an image when exposed to the thermal printing head.
The inventors are aware of third party promotion of the concept of game pieces which may be exposed to a flash of light at point of sale in order to produce an image, and which employ the idea of a thermally sensitive image layer placed over an infrared-sensitive layer for this purpose.